STL containers 2

[maluk]

I need help!
Why won't this work?

deque<ContactInfo>::iterator contact_info_iter;

for(contact_info_iter = contact_list.begin(); contact_info_iter != contact_list.end(); contact_info_iter++)
{
    contact_list.erase(contact_info_iter);
}

Rome did not create a great empire by having meetings, they did it by
killing all those who opposed them.

- janvier -

 

[maluk]

i have a solution but i don't think it is elegant.

deque<ContactInfo>::iterator contact_info_iter;
unsigned int current_contact_count = contact_list.size();

do {
  for(contact_info_iter = contact_list.begin(); contact_info_iter != contact_list.end(); contact_info_iter++)
  {
    if(contact_info_iter->isExpired())
    {
        // Current contact iterator has expired.
        contact_list.erase(contact_info_iter);
        break;
    }
    current_contact_count--;
  }
} while(current_contact_count);

anyone got any more ideas? solutions?

Rome did not create a great empire by having meetings, they did it by
killing all those who opposed them.

- janvier -

 

[ArkM]

Well, how about:

contact_list.erase(contact_list.begin(),contact_list.end());

See also lots of articles with STL deque samples (with el by el erase() too) in MSDN.

 

[chipperMDW]

> Why won't this work?

What's the expected behavior and what's the result you get?

i.e. compile-time error, run-time error, segmentation fault...?


Just so you know, when using iterators in for loops, you should normally use the ++i form of increment instead of the i++ form.

i++ causes the iterator to be copied before it is incremented so that a temporary copy with the previous value can be returned.

++i just increments the iterator and returns the iterator with the new value.

Unless you actually need the previous value, you shouldn't be generating it.

This only applies to user-defined iterators, not built-in ones (i.e. pointers). Still, if you use C++-style iterators at all it's a good habit to get into the practice of using the ++i form all the time unless you really need the behavior of i++.

 

[uolj]

contact_list.clear()

The reason the original code is wrong is because an erase can invalidate iterators in a deque. If you want to remove all elements in the deque, use the clear method above. If you want to remove some elements in a deque, you can use the remove_if algorithm, or a simple loop like this (notice how erase returns the next valid iterator):

std::deque<ContactInfo>::iterator contact_info_iter = contact_list.begin();
while(contact_info_iter != contact_list.end())
{
    if (!contact_info_iter->condition())
        contact_info_iter = contact_list.erase(contact_info_iter);
    else
        ++contact_info_iter;
}